In connection with the spraying, dispensing, or discharge of hot melt adhesive materials, air is routed to the spray modules in order to control the particular patterns of the adhesives being dispensed. More specifically, such air is preheated so as to maintain the adhesive in its heated state such that the hot melt adhesive can properly achieve its adhesive functions. If cooled or ambient air was employed, the hot melt adhesive would experience an inappropriate amount of cooling whereby the utility of the adhesive would be lost. It has also been found to be imperative that the preheated air provided to the plurality of adhesive spray modules be uniform in temperature, density, and flow rate parameters in order to ensure uniformity of the resulting adhesive spray patterns from the adhesive spray modules. Currently, two basic air preheater design systems or arrangements are conventionally in use, however, each one of such systems or arrangements exhibits inherent operational drawbacks or disadvantages.
For example, as disclosed within FIG. 1, a first conventionally known and utilized system is illustrated, is generally indicated by the reference character 10, and is seen to comprise a conduit 12 for introducing incoming air into a heater block 14 within which a plurality of heaters 16,16 are serially disposed. Each one of the heaters 16 may take the form of a conventional spiral tube heater which is illustrated in FIG. 5. As seen in FIG. 5, each one of the heaters 16 comprises an outer housing 18 within which is disposed a hollow aluminum tubular member 20. Tubular member 20 is open at a first left end portion 22 thereof, while the second op-posite right end portion thereof is closed by means of an end face or wall 24 integral with the tubular member 20. The open end portion 22 of the tubular member 20 is provided with an external flanged portion 26 within which a O-ring type seal member 28 is disposed, and the outer peripheral surface of the tubular member 20 is provided with a helical thread or finned structure 30 which extends substantially the entire axial length of the tubular member 20 from within the vicinity of the flanged portion 26 to within the vicinity of the end face or wall 24. An air inlet port 32 is defined within a first sidewall portion of the housing 18 at an axial position adjacent to the flanged portion 26 so as to introduce relatively cool air CAI into the housing 18, and an air outlet port 34 is similarly defined within a second sidewall portion of the housing 18 at an axial position adjacent to the end wall or face 24 so as to permit heated air HAO to exit. It is of course to be appreciated that the helical thread or finned structure 30 cooperates with the interior peripheral surface of the housing 18 so as to in effect define a helical path or conduit along which the air is conducted from the air inlet port 32 to the air outlet port 34. The helical path or conduit provides increased residence time for the air within the heater housing 18 whereby the air is sufficiently heated. In order to provide the heat input for the air, a cartridge type heater, not shown, is axially inserted into the open end 22 of the tubular member 20 and disposed within a heater cartridge cavity 36 defined within the tubular member 20.
Returning then to the system 10 disclosed within FIG. 1, the heater block 14 also has disposed therein a temperature sensor 38 which senses the temperature of the heater block 14 and controls the energization of the heaters 16,16 accordingly. The heated air HAO, after exiting from the heater block 14 is conducted or distributed toward the adhesive dispensing modules 40 by means of a common conduit 42 and a plurality of branch conduits 44,46,48,50. As may readily be appreciated, however, this structural system poses several operative drawbacks or disadvantages. Firstly, it is noted that due to the different distances, for example, of the conduits 44 and 50 from the common conduit 42, relative to the distances of the conduits 46 and 48 from the common conduit 42, non-uniform distribution of the heated air to the various conduits can occur. Secondly, due to the fact that the temperature sensor 38 is in effect embedded within the heater block 14 and is not disposed within the heated air stream, only poor or unreliable temperature control of the air stream is achieved.
With reference now being made to FIG. 2, a second conventionally known and utilized system is illustrated and is generally indicated by the reference character 110. The system 110 is seen to comprise an inlet conduit 112 for introducing relatively cold ambient air into a heated block 114. In particular, the incoming relatively cold ambient air stream 112 is initially divided or distributed into separate air streams which are conducted through branch conduits 144, 146,148,150. The air streams or conduits 144,146,148,150 respectively pass through the heated block 114 such that the separate air streams are heated within the heated block 114. The heated air streams are then conducted by means of the conduits 144,146,148,150 to the adhesive dispensing modules 140.
While the system of FIG. 2 appears to have resolved the problem of dividing the heated air stream into multiple heated branched air streams and the resulting non-uniform distribution characteristics of the same, non-uniform temperature levels or gradients can nevertheless exist within the conduits 144,146,148,150 of the heated block 114 which can of course result in the creation of non-uniform temperature levels within, and heating of, the air streams. In addition to non-uniform fluidic transmission characteristics that may be inherent within the air stream passages defined by the conduits 144,146,148,150, one of the major factors contributing to the creation of such non-uniform temperature levels within the individual air streams and conduits 144,146,148,150 is the embedded disposition of the single temperature sensor 138 within the heated block 114 whereby it is not possible to accurately control the temperature level within each one of the air streams passing through the conduits 144,146,148,150.
A need therefore exists in the art for a new and improved system, and a method of operating the same, wherein the air streams supplied to the dispensing modules can be heated to a desired temperature level, wherein the temperature levels of the air streams supplied to the dispensing modules can be rendered uniform, wherein the temperature levels of the air streams supplied to the dispensing modules can be properly and accurately controlled, and wherein the air stream flow rates provided to the dispensing modules can effectively be rendered uniform.